With recent concerns for volatile solvent pollution in the atmosphere, many studies have been undertaken to determine the safest types of solvents which may be emitted. However, all organic solvents are polluting to some extent and in the final analysis, organic coating systems which utilize a minimum amount of solvent are preferred.
The search for methods of making high solids coatings has been long and difficult. On the one hand, attempts to make extremely high molecular weight non-sintering coatings have involved the use of powder-coating technology, whereby the solvent is driven off by any of several different means, leaving behind a polymeric powder which may then be sprayed onto the coating substrate. This method has been hampered by the difficulties in developing non-sintered polymers and by the expensive equipment needed to prepare and apply these coatings.
It has been proposed in U.S. Pat. No. 3,028,367 to prepare low molecular weight acrylate co-polymers by utilizing organic thiol compounds. However, these products have offensive odors, poor color, and do not stand up well under exterior exposure. In addition, the products prepared require such high amounts of thiol catalysts that the backbone composition of the polymer is substantially modified by the incorporation of the thiol monomer.
U.S. Pat. No. 3,080,348 has suggested that the molecular weight of styrene-acrylate systems may be reduced by increasing reaction temperatures. However, this patent does not involve attempts to prepare molecular weights in the range of those prepared in the instant invention (750 to 5,000), and does not involve tri-component systems as are generally described herein.
It is therefore an object of this invention to prepare essentially solvent-free acrylic resins which exhibit few of the polluting characteristics exhibited by prior art solution and dispersion acrylic systems.
It is another object of this invention to overcome the practical difficulties exhibited by powder coating systems.
It is yet another object of this invention to prepare low molecular weight liquid coating materials which may be utilized at essentially 100 percent solids in presently existing coating application equipment.
Another object of this invention is to prepare low molecular weight acrylate-based polymers having improved exterior durability and odor characteristics.
Yet another object of this invention is to prepare acrylate-based polymers having much lower molecular weight than is suggested in the prior art.